1. Field of the Invention
The present invention relates to a process for growing a thin metallic film and an apparatus therefor. Particularly, the present invention relates to a process and an apparatus for growing a thin metallic film, which is well adapted to metallic wiring and interlayer electrical connection of multi-layer wiring in a semiconductor integrated circuit.
2. Description of the Prior Art
A decrease in the size or width of wirings and an increase in the number of layers in a semiconductor integrated circuit have been demanded in keeping with an increase in the scale of integration thereof. A decrease in the size or diameter of holes (contact holes and through-holes) for electrical connection of wirings between multiple layers has also been demanded. Under such circumstances, it has been increasingly difficult to fill such holes with a metal according to a conventional method such as vacuum evaporation and deposition or sputtering. Further, the decrease in the width of the wiring causes an increase in the current density. A conventional aluminum wiring tends to break due to electro-migration when the current density increases, or due to stress migration. Hence, there is a limit to usage of aluminum for wiring material. Tungsten and molybdenum have a high migration resistance but have such high electric resistance that a semiconductor integrated circuit in which wirings of tungsten or molybdenum are used cannot be operated at a high-speed. Accordingly, realization of a method for forming a copper wiring or gold wiring, each of which has a low electric resistance and high migration resistance, by chemical vapor deposition (CVD) is desired. Especially, a selective CVD method by which a hole is selectively filled with copper or gold is strongly desired.
CVD methods for growth of copper are disclosed in U.S. Pat. Nos. 2,833,676 and 2,704,728. In the both methods, copper is deposited on the whole surface of a substrate irrespective of the material of the surface of the substrate. Hence, aforementioned methods are not suitable to fill a fine hole with copper. Many selective growing methods using CVD have been reported as to tungsten, molybdenum and aluminum.
U.S. Pat. No. 3,697,342 discloses a method of selectively growing copper on a substrate according to CVD. In this method, utilization is made of competitive progress of etching of a substrate material along with deposition of a metal on a substrate. That is, a gas or vapor of hexafluoroacetylacetonato-copper as a starting material is introduced together with hydrofluoric acid or sulfur fluoride as an etching gas in to a reaction chamber to simultaneously cause an etching reaction with the substrate made of boron glass, phosphorus glass or soda glass and a copper deposition reaction on a tungsten, chromium, or silicon oxide film formed on the substrate to thereby selectively grow copper on the given portion of the substrate.
According to the conventional selective copper growth method as mentioned above, however, the shape of a substrate is changed as copper deposition proceeds, because utilization is made of competitive progress of etching of the material of the substrate along with the film deposition as described above. This results in large inaccuracies of the dimensions of the resulting structure, which cannot match with fine processing techniques. Furthermore, according to the conventional selective growth method, it is impossible to selectively grow a metal inside through-holes or contact holes to effect electrical connection between wirings in multiple layers.